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+;; Advent of Code 2020 - Day
+
+(require 'cl-lib)
+(require 'dash)
+(require 'f)
+(require 's)
+
+(setq day8/input
+      (apply #'vector
+             (-map (lambda (s)
+                     (pcase-let ((`(,op ,val) (s-split " " s t)))
+                       (cons (intern op) (string-to-number val))))
+                   (s-lines (s-chomp (f-read "/tmp/aoc/day8.txt"))))))
+
+(defun day8/step (code position acc)
+  (let ((current (aref code position)))
+    (aset code position nil)
+    (pcase current
+      ('() (cons 'final acc))
+      (`(nop . ,val) (cons (+ position 1) acc))
+      (`(acc . ,val) (cons (+ position 1) (+ acc val)))
+      (`(jmp . ,val) (cons (+ position val) acc)))))
+
+;; Puzzle 1
+
+(message "Solution to day8/1: %s"
+ (let ((code (copy-sequence day8/input))
+       (position 0)
+       (acc 0))
+   (cl-loop for next = (day8/step code position acc)
+            when (equal 'final (car next)) return (cdr next)
+            do (setq position (car next))
+            do (setq acc (cdr next)))))